Interest in using mobile and landline/wired computing devices in day-to-day communications has been increasing in recent years. Many of today's wireless data networks comply with Long Term Evolution (LTE) standards for wireless data communications technology. In LTE, the capacity and speed of wireless data networks are increased by using digital signal processing and modulations techniques in the context of an Internet Protocol-based network architecture, yielding significantly reduced transfer latency compared to previous wireless data networks (e.g., 3G).
Recently, a concept called shared cell (also known as “cell merge” or “multi-sector cell”) has been developed in the context of the LTE standard. In contrast to regular LTE deployment, in which each sector is associated with a cell identifier (ID), in a shared cell concept deployment, one cell ID is associated with (i.e., used for) several sectors.
FIG. 1 illustrates a regular LTE deployment, in which each sector 10, 20, and 30 is associated with an individual cell identifier (ID). One cell ID, “Cell A”, is associated with higher power and wider spatial coverage antenna 10 (which may be part of a base station); another cell ID, “Cell B”, is associated with antenna 20; and yet another cell ID, “Cell C”, is associated with antenna 30.
FIG. 2 illustrates an LTE deployment using the shared cell concept in which the same cell identifier, “Cell A”, is associated with antennas 40, 50, and 60.
Two advantages of using shared cell deployment are (1) reduced amount of Cell-specific Reference Signal (CRS) interference in downlinks, and (2) no handover needed when user equipment (UE) moves from one sector to another having the same cell ID.
Shared cell deployments use Spatial Division Multiplexing (SDM) to handle the capacity problem, i.e., to schedule spatially separated users (those who do not interfere with each other), located in the same cell but in different sectors, at the same time. FIG. 3 illustrates an LTE system with shared cell using SDM (antennas 70, 80, and 90 are associated with the same cell ID, “Cell A”). A first communication of UE 85 associated with antenna 80 may occur in the same time slot and the same frequency as a second communication of UE 95 associated with antenna 90 if the respective communications' signals do not interfere. In order to determine which users' communications interfere, powers of the same signal emitted from an individual UE and received in different sectors are measured.
The power measurements indicate in which sector or sectors the UE is located (the UE may be located in several sectors at the same time). That is, if the received power of the UE's emitted signal exceeds a predetermined threshold in a sector, the UE is located in the respective sectors. If two UEs are located in the same sector, they may interfere with each other and, therefore, should not be scheduled at the same time.
Intuitively, one would foresee such power measurements using predetermined reference signals such as a Demodulation Reference Signal (DMRS) or a Sounding Reference Signal (SRS). A description of these reference signals is provided in the current 3GPP documentation (e.g., up to release 11).
Currently, the DMRSs are cell-specific, which means that all UEs in a cell will have the same DMRS, making it impossible to distinguish between UEs in the same cell if the UEs are using the same resources (i.e., frequency and time slot). Although it is possible that, in the future (e.g., devices designed based on 3GPP release 11 documentation), UEs will be able to support UE-specific DMRS, UEs currently in use cannot be distinguished based on the DMRS and, therefore, power measurements cannot be performed using these predetermined reference signals.
The SRS is a UE-specific symbol and, thus, SRS emitted by different UEs can be distinguished from each other. However, emitting SRS uses resources that could have been used for data transmission, which results in reduced data rates.
Accordingly, it would then be desirable to provide methods and devices for estimating the power of UE signals received in different sectors without using reference signals.